The progenitors of subluminous type Ia supernovae

We find that spectroscopically peculiar subluminous Type Ia supernovae (SNe Ia) come from an old population. Of the 16 subluminous SNe Ia known, 10 are found in E/S0 galaxies, and the remainder are found in early-type spiral galaxies. The probability that this is a chance occurrence is only 0.2%. The finding that subluminous SNe Ia are associated with an older stellar population indicates that for a sufficiently large look-back time (already accessible in current high-redshift searches) they will not be found. Due to a scarcity in old populations, hydrogen and helium main-sequence stars and He red giant stars that undergo Roche lobe overflow are unlikely to be the progenitors of subluminous SNe Ia. Earlier findings that overluminous SNe Ia [Deltam(15) (B) less than or similar to 0.95] come from a young population are confirmed. The fact that subluminous SNe Ia and overluminous SNe Ia come from different progenitor populations and also have different properties is a prediction of the CO white dwarf merger progenitor scenario.